Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.64	4.248%	$89.278	$89.28	$89.30	$89.30
Purchase #2	$188.46	10.813%	$208.8382	$208.84	$208.85	$208.80
Purchase #3	$224.79	8.352%	$243.5645	$243.56	$243.55	$243.60
Purchase #4	$148.68	9.730%	$163.1466	$163.15	$163.15	$163.10
Purchase #5	$152.97	8.620%	$166.156	$166.16	$166.15	$166.20
Purchase #6	$172.81	12.787%	$194.9072	$194.91	$194.90	$194.90
Purchase #7	$30.88	11.845%	$34.5377	$34.54	$34.55	$34.50
7 purchase totals =	$1,004.23		$1,100.4282	$1,100.44	$1,100.45	$1,100.40